Autopsy showing police shot a black teen in the back could escalate tensions in St. Louis

Barbara (L) and Dennis Ball-Bey, the parents of Mansur Ball-Bey, stand with their niece Shawnetta (R) on the steps where Mansur was shot in St. Louis, Missouri, United States, August 20, 2015. Reuters/Lawrence Bryant (Reuters) - An autopsy on the body of the black teenager shot and killed by white St. Louis police officers this week shows the 18-year-old died from a single gunshot that entered his back and struck his heart, a medical examiner said on Friday.

The finding could escalate tensions that flared immediately after the shooting Wednesday, as protesters and family members of the slain teen questioned police accounts that Mansur Ball-Bey pointed a gun at officers.

The results of the autopsy show Ball-Bey was struck in the upper right part of his back by a bullet that hit his heart and an artery next to the heart, said St. Louis Chief Medical Examiner Michael Graham.

That and other findings from the autopsy appear to contradict the account of the incident given by police, who said that two officers shot at Ball-Bey when he pointed a gun at them as he fled a home where police were serving a search warrant. Police said that Ball-Bey dropped his weapon and continued running after he was shot.

The shooting sparked angry clashes between residents and police Wednesday night, with officers turning out in riot gear and using tear gas on some protesters. More protests are planned for Friday night in the area of the shooting, according to social media posts by activists.

The flare-up came less than two weeks after the St. Louis area was flooded with protesters from around the country marking the anniversary of the Aug. 9, 2014, police killing of unarmed black teenager Michael Brown by a white police officer in nearby Ferguson, Missouri.

The position and track of the bullet - which did not exit Ball-Bey's body - show that the teen's body was not turned toward officers when he was shot, Graham said. The shot would have killed him nearly instantly, making it difficult if not impossible for him to continue running after he was shot, though if he was running there would have been some forward momentum, Graham said.

James Cody (L) and his cousin Dennis Ball-Bey attend a candlelight vigil for Mansur Ball-Bey in St. Louis, Missouri, United States, August 20, 2015. Reuters Graham said it was impossible to tell from the autopsy whether or not Ball-Bey was slightly turned, or was twisting his torso toward officers when he was shot.

"There are so many variables," said Graham. "But he certainly wasn't facing, his chest wasn't facing the officers."

The results of the autopsy are preliminary and an investigation of the incident continues, police said in a statement.

St. Louis Police Chief Sam Dotson told the St. Louis Post-Dispatch newspaper that the location of the fatal wound neither proves nor disproves the account given by the two officers who said they fired four rounds at Ball-Bey.

Police said they recovered a gun and determined it was stolen, but Jermain Wooten, an attorney representing Ball-Bey's family told CNN on Friday that no witnesses had seen the teenager with a gun.

Wooten said Ball-Bey did not live in the community and was in the area visiting relatives, but not at the house where police were serving the warrant, he said.

"He never had a gun. He did not point back toward the officers," Wooten told CNN. He said Ball-Bey could not have run more than a few feet after being shot, which contradicts police statements.

A report containing evidence gathered in Ball-Bey's shooting will be turned over to the city attorney and the U.S. Attorney in St. Louis for review, police officials said.